Yep, it's just cargo now. IIRC, many of the existing mail/RPO contracts were cancelled together in 1967. This eliminated the last significant income source from passenger rail other than sharply declining ticket sales. By this time, the REA was also a fading shadow of itself (although it struggled on a few more years.) The last RPO operated on the Northwest Corridor and came off in the mid-70s.

I meant to also comment that the 67 mail contract cancellations were part of the forces that led to the formation of Amtrak. People still needed passenger rail, but the old model of subsidzed-by-freight, mail, express was no longer working. Thus Amtrak, which also absolved participating RRs of their charter/contractual passenger obligations en masse. Still trying to get people used to the idea that passenger rail requires some level of support from the government like it does everywhere else in the world, we'll figure passenger rail and how to support it out eventually. Dense urban corridors are becoming undriveable in reasonable amounts of time and not everyone can afford a helicopter

Presidents come and go -- and JFK was gone 4 years by 1967 -- but the economic, technological, and other social forces that undermined passenger trains were unrelenting. Eisenhower's enthusiasm for the Interstate system was a big factor in the death of passenger trains and the shift to not just air, but trucking to move mail. RRs were faster than trucks until the interstate came along. Afterwards, it was usually no contest. With passenger trains fading, it was even harder or the PO to get mail moved when and where it needed. A cascade of shifting circumstances tends to argue against any individua's sole responsibility, even the president's.

On-line you can find scanned images of magazines from the 1920s, 30s etc., like Popular Science et.al. Almost every issue has several small ads throughout the classifieds with an image of an RPO (photo or drawing) having copy along the lines of "Want A Steady Job? Railway Postal Clerks - Mail Carriers". Salary range listed in a June 1930 ad was $1,700 to $3,300 a year (25K to 48K inflation adjusted - not bad for the Great Depression).

Of course, from my early 21st century perspective I have no concept of how mailing in a coupon to a private concern (for example, in the ad I mentioned above, the Franklin Institute - obviously not the Philadelphia museum) to get a catalog listing said government jobs is not going to be a scam. The drawings of the RPOs OTOH over the year range from normal to rather hilarious looking bizarre 'streamlined' monstrosities...

Depending in when you think the "interstate twinkle" started for Ike personally, that could be anywhere from immediately after WWI to WWII to the 1950s.

Ike served with what was IIRC the Army's first coast-to-coast march right after WWI. The roads could have been better.

During WWII, Ike observed the strategic significance of the German autobahns, right down to turning them into emergency airfields during wartime. That's why some sections of the interstate out west (Kansas, Nebraska, etc) have at least 5 miles of straight highway between overhead bridges. Yep, a B-52 field in a pinch.

True enough RPOs were being cut back after WWII. Improving roads and quickly growing airlines offered alternatives the Post Office eagerly picked up on. But the RPO still served on largely unchanged except for those that were withdrawn from service. One thing that looked only a little different than RPO service was the growth of storage mail, often using headend cars quite similar to RPOs or converted from them to this service by the removal of sorting racks, etc.

RPOs were being cut back after WW2 but I don't think they were 'dying'. Well into the 1950's-60's the top train on the Great Northern was the Fast Mail - it was considered a better / more prestigious run for an engineer than the Empire Builder. Mail contracts generally made the difference between passenger trains losing money vs. at least breaking even. Once the mail went off the rails, many passenger trains were discontinued as losing ventures.

Like HPOs (Highway Post Offices). Oddly, RPOs outlasted the last HPO route by about 3 years, but it was the change in US postal operational policy to using central mail sorting/distribution centers that more or less doomed both concepts.

Peaked in 1948 with nearly 800 lines. Within 15 years, there were less than 250. That's a freefall, not even a slow decline.

With any transportation system, you have to be careful about drawing meaning from raw numbers. Sure, the number of routes was down significantly. Cutting off low volume RPOs was a relatively easy economy move. It likely bought time and resources that sustained the rest.

And the rest that survived were most likely the high volume routes. I have no idea what the actual numbers were, but it wouldn't surprise me if the loss 500+ RPOs resulted in only a 20% drop in the volume of mail that was handled by the RPOs. That's just a guess (anyone with some data know better?), but it points out how this and other issues add complexity to the fading out of the RPO.

Another example is something people often don't associate with the downfall of the RPO, but which was an essential part of their existence. They sorted the mail as the train rolled along. I don't know much about the PO's history of experimenting with machine sorting. The Zip Code? An essential part of machine sorting, few blame the lowly Zip Code for the demise of the RPO, but it played a role as it was brought into action in the early 60s. But however things went with automating sorting, they weren't going to put one of those on a train. Nope, the whole system was being revamped in the process of generally modernizing the RPO out of existence. It's less a story about who to blame or of failure than it is of obsolesence.

Mike makes a great point, most likely many of the RPO routes that were cancelled in the '50's - '60's were small branch line operations...probably being served by a passenger car or RDC with a 15' RPO section. Many of these trains were being cut back for lack of riders anyway.

The last working mail train cover is a real beaut, and if I owned it, it would be in a shadow box!

If you're ever in Baltimore, the B&O Museum has a wonderful short video in their old Ma & Pa mail-baggage car about the Railway Mail Service. They have stories from a lot of old RPO clerks, including one elderly gentleman who reminisced ab riding the last working mail train. When I hired on the railroad a decade back, a lot of the old timers still referred to 190 (the 3:15 out of Washington) as "the mail train," although I am not entirely sure whether that's a reference to RPO service or the later practice of hauling bulk mail. Fred Frailey's "Zephyrs, Chiefs, and Other Orphans" has a section on the NEC mail service which is worth reading (my recollection is that it got overlooked when the NEC was transferred from PC in 1976, and the recipients were a little surprised to find that they owned it).